In the related art, since a capacitive fingerprint detection circuit in a chip has advantages of small size and low power consumption, this kind of fingerprint detection circuit is more preferred in a market of mobile phones and tablets.
The above capacitive fingerprint detection circuit detects fingerprint ridge information and fingerprint valley information. Since the distance between the fingerprint ridge and a sensing unit of the fingerprint detection unit is relatively close, and the distance between the fingerprint valley and the sensing unit of the fingerprint detection unit is relatively far, there is a difference between a ridge capacitance generated between the fingerprint ridge and the sensing unit and a valley capacitance generated between the fingerprint valley and the sensing unit. Once the ridge capacitance and the valley capacitance (referred to finger capacitance hereinafter) are detected, ridge characteristic and valley characteristic may be analyzed.
A voltage output from the above fingerprint detection circuit has a proportional linear relation with the finger capacitance (capacitance to be tested). A final result has a small difference between an output voltage corresponding to the finger capacitance of the ridge and an output voltage corresponding to the finger capacitance of the valley, so that it needs to amplify an output voltage corresponding to the finger capacitance by a predetermined factor for processing, in which the predetermined factor is generally a fixed value set based on experience. However, each person's finger is different, and thus the fixed predetermined factor will affect the accuracy of the final result.